Corrosion inhibition



May 19, 1964 M. F. KELLEY, JR 3,133,787

CORROSION INHIBITION Filed Sept. 4, 1962 O.2I49g OF THE Z-BUTOXYETHYL ACID PHOSPHATES OF EXAMPLE IIb) ACTUAL CURVE OBTAINED ON POTENTIOMETRIC TITRATION IN A 60-40 ACETONE-WATER SOLUTION.

3 4 5 6 7 8 9 IO II I2 I3 ml. of 0.!076 N NOOH IN V EN TOR. MATTHIAS FRANCIS KELLEX JR BY hwgmw, J x

TTORNE Y United States Patent 3,133,787 CORROSION l 1 in:

Matthias Francis Kelley, Jr., Richmond, Va., assignor to Socony Mobil Oil Company, Inc., a corporation of New York FiledSept. 4, 1962, Ser. No. 221,940 32 Claims. (Cl. 21-2.7)

changers, and other types of cooling apparatus are subject to a gradual corroding action which eventually interferes with the operation of and may shorten the life of the equipment. While many anticorrosive agents, per se, are known, very few have the necessary characteristics of being stable under normal operating conditions of the systems, and performing eflioiently over long periods of time without decomposing or forming insoluble deposits within the systems. 7

"For example, some of the more commonly used agents for preventing rust formation on ferrous metals are the diethylamine and urea addition products of mixed poctylphenyl acid phosphates. While these agents are satisfactory for ferrous surfaces, they are unsatisfactory for use in the protection of aluminum surfaces in con tact with aqueous coolants because they form undesirable, thick deposits on the aluminum. Furthermore, these corrosion-inhibitingagents cloud the liquid coolant with insoluble solids which have detrimental effects on the pumping and circulatory system of the apparatus in which they are used.

It is, therefore, an object of this invention to provide corrosion inhibitors which obviate the aforementioned disadvantages.

, It is another object of this invention to provide corrosion inhibitors for metals which are stable for long periods of time in aqueous mediums, and which do not decompose to form harmful deposits either on the surface of the metal or in the aqueous medium in contact with the metal.

It is a further object of this invention to provide a method for inhibiting the corrosion of aluminum surfaces in contact with an aqueous medium by effecting the contact in the presence of a corrosion inhibitor comprising the reaction product of an organic amine with an acid mixture which is the reaction product of phosphorus pentoxide with an alkoxyalkanol.

'In attaining the objects of this invention, one feature resides in treating metal surfaces, particularly aluminum surfaces, 'with an organic amine salt of an alkoxyalkyl acid phosphate mixture, such as the diethylamine salt of a mixture of butoxyethyl dihydrogen phosphate and his (butoxyethyl) hydrogen phosphate.

Other objects, features, and advantages of the invention will become more obvious from the following description thereof:

It has been discovered that the corrosion of aluminum in contact with an aqueous medium may be inhibited if there is present in the aqueous medium an effective amount of an acid mixture represented by the formula wherein R is a member selected from the group consisting of a lower alkyl radical, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, heXyl, etc., a lower alkoxy-substituted lower alkyl radical, and a benzyl or phenyl radical; x is either 2 or 3; and y and 2 each represents an integer selected from the numerals 1 and 2 and the sum of y and z is 3.

Included among the acid mixtures coming within the scope of the above formula are 2-butoxyethy-l acid phosphates, Z-ethoxyethyl acidphosphates, Z-methoxyethyl acid phosphates, Z-methoxyisopropyl acid phosphates, 2- (Z-ethoxyethoxy) ethyl acid phosphates, 3-(3 -methoxypropoxy) propyl acid phosphates, 3-[3-(3-methoxypropyl) propoxy] propyl acid phosphates, Z-(Z-methoxyethoxy) ethyl acid phosphates, and 2-benzyloxyethyl acid phospha-tes.

While the acid mixture itself has been found to be an effective corrosion inhibitor for aluminum surfaces, it is a further discovery that the products obtained by reacting the aforesaid acid mixture with an organic amine, including alkyl amines having from 1 to 14 C atoms and alkanol amines, such as diethylamine, dipropylamine, diisopropyl amine, butylamine, dibut-ylamine, isobutylamine, t-C12H25NH2, t-C QII NH @thar nolamine, diethanolamine, triethanolamine, etc., high molecular weight primary amines including abietyl amine and dehydroabietyl amines, and mixtures of these amines, produce unexpectedly superior results than when the acid mixture alone is used as the corrosion inhibitor.

Generally, the acid mixture is prepared by the addition of an equivalent of phosphorus pentoxide, P20 to three equivalents of an .alkoxyalkanol, such as buty=l Cellosolve (C H OCH CH 0H), substantially as shown by the following equation:

C4Hu0 CHZCHZOH P205 (041190 CH2CH2O)zP (O) OH 0. 1190 OHiOH O P (O) (OH M An active amine addition product can be prepared from this acid mixture substantially as indicatedvby the following equation:

' ll oimocmomo P (OH)2 These equations represent the acid-amine salt mixture obtained from using suflicient amine to react and bind with the primary acid function or primary acid hydrogen Whereas it is believed that the amine present in excess of the amount to bind the primary acid hydrogens of the mixture to be free amine, it is possible that it is very loosely bound to the secondary acid hydrogen. If the latter is the case, the bond is highly unstable, for when the acid-amine product (containing free or loosely bound amine) is subjected to vacuum and gentle heat, the amine above that required for the primary acid hydrogens is always recovered.

The relative quantities of monoand dibasic acid can be found by potentiometric titration which gives a curve of the type illustrated in the figure of the drawing. From this curve the quantity of amine necessary to prepare the desired compound can be determined.

For example, a good corrosion inhibitor is obtained when an amount of amine equivalent to Y in the figure is added. An active inhibitor is also obtained when a quantity of amine equivalent to any point between X and Y is present. An even moreetfecti-ve inhibitor is realized when the amount of amine added to the mixed acid produ'ct corresponds to Z. The amount of amine needed for Z is calculated as follows:

where X, Y, and Z are the equivalent quantities of base required to neutralize the acid corresponding to each individual point. The preferred reaction product of the 2- butoxyethyl acid phosphates, as well as the other mixed acids of the invention, contains an amine concentration equivalent to this point.

i The acid-amine products of this invention, as indicated by the foregoing discussion, may be acidic, basic, or substantially neutral according to whether the amount of amine corresponds to X, Y, or Z. Obviously there are varying degrees of acidity or basicity depending upon whether the amount of amine present is equivalent to a point between X and Z or between Z and Y. All of these materials are useful in preventing corrosion. is evidenced by the fact that these acids (as for example 2- butoxyethyl acid phosphates) containing amine equivalent to points X and Y give corrosion inhibiting values averaging about R- and R-3, respectively, on aluminum (see Example IV and the discussion before Table III for the meaning of these R values) Thus, considering the mixture of monobasic and dibasic acid as having three acid functions, the reaction therewith with two equivalents of amine binds the primary acid hydrogens, corresponding to point X on the graph of the figure. If three equivalents of amine are added to the acid mixture, then all of the acid functions will have amine bound thereto, assuming that a loose bond occurs with the secondary acid hydrogen. In any event the three equivalents of amine correspond to point Y on the graph of the figure. Point Z is obtained by use of 2 /2 equivalents of amine which is sufficient to bind all of the primary lacid hydrogens of the acid mixture and an excess of /2 equivalent of amine is present as free amine or loosely bound to one half of the secondary acid hydrogens.

A graph such as that illustrated in the figure is representative of a potentiometric titration curve. When water is the medium, the point Z occurs at a pH of about 7. Indicated pH systems other than water are always above the true pH. Thus whatever the system used for titration, the intervals on the curve are the same. Also, regardless of the titrating medium the X, Y, and Z points determine the quantity of amine to be used and the Z point gives a substantially neutral acid-amine product.

The following examples illustrate methods of preparing the aforementioned acid mixtures and the dialkylarnine salts thereof, but it must be understood that the examples are merely illustrative and are not to be considered as limiting, in any manner, the scope of the invention.

4 EXAMPLE 1 Preparation of the Mixed Bntyl Cellosolve Phosphates (a) 335 parts of butyl Cellosolve were placed in a reaction vessel fitted with a stirrer, thermometer, and rubber sleeve for solids addition. 142 parts of P 0 were placed in another vessel suitable for attachment to the rubber sleeve provided for solids addition. While stirring, the P 0 was added, rapidly at first to bring the reaction temperature to 6570 C. The rate of addition of the P 0 to the butyl Cellosolve was then regulated so that very little cooling was required to maintain this 65-70 C. reaction temperature. Upon completion of the addition of the P 0 the reaction mixture was stirred for 30 minutes without heating or cooling. Following this period, the stirred mixture was heated to 68-72" C. and was maintained there [for three hours. Filter aid was stirred into the product, and the mixture was filtered while still hot. The product had an index of refraction at 25 C. of 1.4397, n specific gravity (20/4) of 1.124, and a total acid No. of 333.5. The theoretical total acid No. for this product is 338.9.

(b) 3191 parts of butyl Cellosolve and 1278 parts of P 0 were placed in vessels as described in (a) above. While stirring, the P 0 was added to the butyl Cellosolve, cooling to maintain the reaction temperature at or below 20 C. When the P 0 addition was complete, the cooling bath was removed and the temperature was allowed to rise to 30-35 C. Heat was then applied, and the temperature of the stirred mass was raised to C. and was maintained there for about five hours.

The product has the following properties: index of refraction of 1.4412 at 23 C.; specific gravity (20/4) of 1.156; total acid No. of 329.3. The theoretical acid No. as in (a) above is 338.9

EXAM PLE II Preparation of the Diethylamine Addition Product of the Mixed Acids of I A sample of the mixed acids of Example 1(a) was titrated potentiometrically to determine the quantity of diethylamine required to react with the acid content corresponding to the point Z in the figure. It was found that 33.2 parts of diethylamine were needed for parts of the mixed acids.

100 parts by weight of the mixed acids of Example 1(a) were added to a suitable reaction vessel fitted with a means for liquid addition, a stirrer, a condenser, and a means for determining the reaction temperature. 3312 parts by weight of diethylamine were added to the mixed acids at 45-50 C., and stirring at this temperature was continued for 45 minutes to complete the reaction. The product was a dark brown liquid and had an index of refraction of 1.4451 at 25 C. It contained 9.67% P and 4.57% N (theor. 9.36% P, 4.78% N).

The following examples are merely illustrative of the corrosionand deposit-inhibiting effects of the compounds of the invention on aluminum and steel surfaces. Again, it is to be understood that the methods employed and the quantities and kinds of agents used are merely for the purpose of illustration and the invention is not to be considered limited thereby.

An effective amount of the amine salt of the acid mixture was added to a 2.5:1 water-ethylene glycol mixture, and the metal to be tested was immersed in the solution. The corrosion-inhibiting effects of the agents were determined under both static and dynamic conditions, and the tests were run at elevated temperatures to accelerate results which would be obtained normally over longer periods at room temperature. The elevated temperature tests also give good indications as to the ability of the agents to withstand the effects of prolonged high-temperature operation. The improved results were measured in terms of the improved appearance of the metal surface compared with that of the metal surface immersed in a controlled solution containing no additive. The improved results were also measured in terms of a lack of insolubles in the coolant liquid.

EXAMPLE HI Inhibition of Corrosion of Aluminum-Static System The following test solutions were prepared from ethylene glycol, water, and additive. The ethylene glycolwater mixture ratio is 1:2.5, and the parts are parts by weight.

99.88 parts of ethylene glycol-water,

0.12 part of a commercial inhibitor, a mixture of v 99.88 parts of ethylene glycol-water,

0.12 part of a second commercial inhibitor, the urea salt of octylphenyl acid phosphates.

99.88 parts of ethylene glycol-water,

0.12 part of my product of Example II.

100.00 parts of ethylene glycol-water (control).

Each of these solutions was placed in a suitable container. Squares of aluminum one inch on a side and about one-sixteenth of an inch thick were cleaned with acetone, and one square was placed in each of the four solutions. These solutions containing the aluminum squares were placed in an oven at 90 for a period of It will be noted from the above table that even though the prior art corrosion inhibitors did not cause pitting, the heavy precipitate in the solution and on the aluminum surface itself makes them unsatisfactory for inhibiting the corrosion of aluminum.

EXAMPLE IV Inhibition of Corrosion of Aluminum and Steel- Dynamic System In testing the corrosion-inhibiting effect of agents of this invention on aluminum and steel in a dynamic system, a modification of the procedure outlined under ASTM D665-49T or D665-50T, Rust Preventing Characteristics of Steam Turbine Oil in the Presence of Water, was followed with ethylene glycol-water being used in place of the recommended mineral oil and sea water. The steel used was the standard specimen required as defined in the two ASTM references. The aluminum used in these tests, as well as those subsequently to be described, was aluminum alloy 1100 F. which contains a of 99% aluminum and minor amounts of copper, silicon, iron, manganese, and zinc. The test was run for seven days rather than twenty-four hours. The ratings of the effects of steel were based on a visual scale, R-l to R-7, where R-l is defined as free of rust and R-7 is defined as surface covered with a heavy rust layer. This scale (R-l to R-7) for steel is a modification of the reporting procedure recommended in the references. The scale used is as follows:

R-1 Free of rust.

R-2 Trace of rustfew spots.

R-3 Less than 5% of surface rusted. R-4 5% to 50% of surface rusted. R-S 50% to 99% of surface rusted. R-6 Surface covered with light rust. R-7 Surface covered with heavy rust.

The effects of the agents of the invention on the aluminum metal and on the liquid in contact with the metal were measured as shown under Example III.

A stock solution containing 92 parts of ethylene glycol and 228 parts of water was prepared. The solution was divided into eight equal parts, each was placed in a suitable container provided with a means for stirring, and the formulation of Example II was added to these parts so that two of them contained 0.10%, two contained 0.25%, and two contained 0.5% by weight. The other two were controls containing no additive. The solutions were heated to 60 C. Polished steel bullets (ASTM D665- 50T, ASTM Standards, 1950 supplement, part 5, page 191) of the same size were immersed in the other set. Stirring of the solutions in which the metal pieces were immersed was maintained continuously fora period of seven days at the 60 C. temperature. At the end of the seven days, the results were noted and recorded as follows:

TABLE II Steel Aluminum Additive, Parts of Etching Condition Condition percent of additive Rating or of of solution to basic pitting solution sample solution 0 R-7 Deep Clear No coating.

pitting 0. 32 R-l None do Do. 0.80 R-l do do Do. 1. 60 R-l do do Do.

While from 0.1 to 0.5% by weight of the neutral reaction product of Example II was used for purposes of testing, amounts of the formulations of this invention outside of this range will perform satisfactorily, i.e., concentrations of the active ingredient in the range of about 0. 04l.0% and above are effective but no increased corrosion inhibiting activity is noted by exceeding the upper limit of the preferred range.

Further amine-acid reaction products which have been found to be effective corrosion inhibitors for metals are summarized in the following table. They were prepared in accordance with the procedure outlined in Examples I and II.

The products of Table III were tested on aluminum and/or steel as outlined in Example IV for aluminum and steel and at temperatures of C. and 60 C., respectively. The R ratings for aluminum refer to the amount of pitting on the surface of the metal. The

following scale was used in rating these metals:

R-l Free of pits.

R-2 1-5 small pits 1 mm. or less in diameter the remainder of the surface bright.

R-3 6-15 small pits 2 mm. or less in diameter the remainder of the surface bright.

R-4 '1'630 small pits 2 mm. or less in diameter.

R-S 31 or more pits 2 mm. or less in diameter.

R-6 10% of surface pitted with pits larger than R-7 20% or more of surface pitted with pits larger than 2 mm.

i In every case involving a control, the control sample was pitted over or more of its surface. In none of the tests involving the compounds was there significant amounts of deposits, either on the surface of the metal or in the coolant solution.

3 EXAMPLE v Into each of four standard paint cans 100 grams of a conventional latex paint formulation was added, 14.5 grams of aluminum pigment, and 1% by weight of a A 1:1 ethylene glycol-water mixture was used as the corrosion inhibitor, and the mixture blended until the aqueous medium in the tests involving the compounds pigment was suspended therein. A lid was pressed onto of Table III. each can under a pressure of 200 lbs. and the sealed cans TABLE III Percent P Percent N No. Acid mixture Amine uscd nw) 4 Alumi- 11 Steel num Calc. found Cale. found 1 2-methoxyethyl acid phosphates Dicthyl 1.4474 (24) 1.158 11.31 11.82 6.21 6.18 R-l 2 Z-ethoxycthyl acid phosphates 1.4455 (24) 1.113 10.51 10.43 5.76 5.44 R-2 3 2-benzyloxyethyl acid phosphates 1.5078 (26) 1.175 3-00 8.07 4.35 4. R-l R-l 4 2-(2-methoxycthyoxy)ethyl acid phosphates 1.4533 (23. 5) 1.167 9.13 9. 66 4.96 4. 78 R-2 5 2-(2-ethoxycthoxy)ethy1acid phosphates 1.4535 (23. 5) 1.147 8. 68 8.62 4.54 4.42 R-4 R-l 6 2-(2-but0xyethoxy)ethyl acid phosphates 1.4500 (23.5) 1.098 7. 72 7.96 4.17 4.08 R-2 R-4 7 Z-methoxyisipropyl acid phosphates a 10. 10.45 5. 84 5. 47 R-2 R-l 8 3-(3-methoxypropoxy)propyl acid phos- 1.4449 (23.5) 1 058 8.08 8.36 4.50 4.51 R2 R-2 phates. 9 3-[3-(3-methoxypropoxy)propoxy)]propyl 1.4460 (23.5) 1.080 6.64 6 79 3.53 3 63 R-2 acid phosphates. 10 2-butoxyethyl acid phosphates D1pr0py1 1.4425 (26) 8.34 8.06 4. 59 4.47 R-l R-l 11 do Diisopropyl 1.4485(26) 8.34 8.40 4.59 4.54 R1 R-l Butyl 1.4455 (26) 9.18 9.18 5.06 4.93 R-l R-l Isobutyl 9. 18 9. 26 5. 06 4. 97 R-1 R-l Dibutyl 7. 64 7. 51 4. 20 4. 24 R-l R-l Diethan0l 1.4656 (26) 1.133 8.24 8. 55 4.53 4. 60 R-l R-l Primiene 81R 1. 4566 (23) 1. 133 6. 76 6. 66 3. 71 3. 68 13-1 R-l an dipropyl. Primene 81R 6. 66 6. 51 3. 66 3. 62 R-l R-2 and dihutyl. 18 dn Amine D and 5. 34 4. l9 2. 97 3. 42 R-l R-l dipropyl.

While the products of the invention are excellent corwere placed in storage at room temperature. Two con-' rosion inhibitors for aluminum and steel surfaces which are exposed to an aqueous medium, such as in a cooling system, the products may be coated on to the aluminum and steel surfaces so that when exposed to humid conditions, corrosion of the surfaces is inhibited.

Amine-D is a product of Hercules Powder Company and is described in its Technical Bulletin 217 as being predominantly high molecular weight primary amines composed of abietyl amines with major ones being dehydroabietyl amines. Primene 81R is principally a mixture of t-C H NH and t-C H NH In the above examples of Table III, wherein these amines were used in conjunction with lower molecular weight amines, Primene 81R and Amine-D were added to the point X of FIGURE 1, and the other amine in a quantity corresponding to the difierence between X and Z.

It has also been found that the corrosion inhibitors of the present invention may be successfully utilized with compositions containing water and aluminum pigment, such as aluminum pigmented paints. Many of these paints are formulated in the presence of water and when the paints are placed in conventional cans or container, the aluminum, in the presence of the water, slowly corrodes and hydrogen is formed. Unless this corrosion is inhibited, thereby substantially decreasing or eliminating the evolution of hydrogen, sufficient pressure builds up to either bulge the cans, raise the lids from the cans, or rupture the sealed cans or containers. While diammonium phosphate is presently used for inhibiting the corrosion of aluminum pigment in paints, it is not as effective over long periods of storage as are the inhibitors of the present invention.

trol cans containing no inhibitor were also placed in storage. Each can was examined daily and the results of the storage tests are set forth below:

TABLE IV.EFFEOT 0F INHIBITORS ON THE STORAGE OF ALUMINUM PIGMENTED PAINT FORMULA- I No rupture after;

Good results were also obtained when diethylamine salt of the mixture of butoxyethyl dihydrogen phosphate and bis(butoxyethyl) hydrogen phosphate was used as the corrosion inhibitor in place of the corresponding hexoxyethyl acid phosphates.

It appears that the presence of a minor but sufiicient amount of the corrosion inhibitor of the invention in aluminum pigmented paints, containing some water due to their formulation, is sufiicient to prevent corrosion of the aluminum powder and thus prevent the evolution of hydrogen within the paint container.

While from 0.04 to 1% by weight of the corrosion inhibitor of the invention is preferred, based upon the weight of the liquid composition, more than 1% can also be used, but the improvement in corrosion inhibition is not markedly improved thereby. While the above paint formulation had 12.5% aluminum pigment therein, it is I l l readily apparent that the amount of corrosion inhibitor to be used will depend upon the amount of aluminum pigment and water which are present in the composition. The amount of inhibitor sufficient to inhibit the corrosion of the aluminum pigment in the presence of the Water can readily be ascertained.

The corrosion inhibitors of the present invention have also been found useful in processes for anodizing and sealing metal surfaces, including aluminum and magnesi um surfaces. For example, in the known processes for bright-dipping aluminum, the aluminum sheet or article is subjected to the reaction of an aqueous solution of a mixture of a major amount of phosphoric acid and a minor amount of nitric acid, i.e., by immersing the aluminum into the acid bath at a particular temperature for a period of time sufiicient to brighten the surface thereof, but insufficient to harmfully attack the metal.

Most commercially available acid baths for polishing aluminum comprise about 52-94% phosphoric acid, 1- 18% nitric acid and from 530% water. Acetic acid or other acid or salt additives may be present in minor amounts. The bath is maintained at a temperature of from 150 F. to the boiling point of the mixture, preferably within the range of 170200 F., and the aluminum article is immersed for a period of from a few seconds to several minutes, until the surface of the article is brightened. Processes for bright-dipping aluminum include those disclosed in Cohn Patent 2,729,551 and in copending application Serial No. 860,730, filed December 21, 1959, now abandoned, and these processes are incorporated herein by reference.

The brightened aluminum articles may be anodized by any of the conventional processes, including using direct current and acids or other electrolytes, and this anodizing treatment is followed by the conventional sealing treatment.

For example, an aluminum sheet which has been brightdipped in the manner described above is first rinsed in water and then immersed in an anodizing bath of sulfuric acid, usually 12-20% by volume, and water, and maintained at room temperature. After rinsing, the anodized metal surface is then sealed by immersing in hot Water, i.e., at a temperature of from about 175 F. to 212 F. until a hydrated aluminum oxide coating is formed on the surface of the metal. This occurs in from about 5 to 30 minutes, depending upon the metal surface being treated and the temperature of the sealing bath.

While this hydrated oxide coating protects the aluminum surface, it breaks down under adverse conditions such as weathering, exposure to salt water sprays, and the like. It has been found that the corrosion inhibitors of the present invention are useful in protecting the anodized metal surface against the adverse effects of moisture, salt water sprays, weathering, and the like. It has also been found that when the anodized aluminum or magnesium sheet is immersed in an aqueous solution containing from about 0. 15 to 0.25% of the corrosion inhibitor of the invention either prior to or after the aforesaid sealing step, and preferably both before and after the sealing step, the sealed anodized surfaces thereof are extremely resistant to corrosion by moisture, water, salt water sprays, weathering, and the like.

EXAMPLE VI A series of five aluminum panels of identical size were buffed and then bright-dipped in an aluminum polishing bath comprising a mixture of 94 parts by volume of 85% phosphoric acid and '6 parts by volume of concentrated nitric acid at a temperature of 200 F. for a period of 2 minutes and 15 seconds.

One panel was then anodized by immersing it in an anodizing solution of about 16% sulfuric acid and water at a current density of 12 amperes per square foot. The anodized surface was then sealed by immersing the panel in water at a temperature of 205 F. for a period of about 20 minutes.

A second panel was treated in a manner similar to the first panel, except that it was immersed in a 0.15% by weight solution of diethylamine salt of a mixture of butoxyethyl dihydrogen phosphate and bis (butoxyethyl) hydrogen phosphate for a period of about 1 minute prior to the sealing of the panel surfaces by immersion in the hot water.

A third panel was treated in the same manner as the first panel except that it was immersed in the same phosphate solution as the second panel for a period of about one minute before and after the sealing of the panel surfaces by immersion in the hot water.

The fourth panel and fifth panel were also treated in the same manner as the first panel, except that both were immersed in a 0.25% by weight aqueous solution of the diethylamine salt of the butoxyethyl acid phosphates of the invention for a period of 1 minute prior to sealing the surfaces with the hot water. The fifth panel was then again immersed in the 0.25% solution of the corrosion inhibitor for an additional '1 minute period. 7

All five anodized aluminum panels were subjected to a continuous salt spray for a period of 250 hours, and the surfaces of each panel were examined. a g

The surface of the first, i.e., the control panel had a dull, cloudy appearance, and its original brightness had been substantially lost. The second and fourth panels had lost only a minor portion of their original specular reflectance and presented a vast improvement over the appearance of the control panel. The third and fifth panels had the same specular reflectance as they had prior to being subjected to the salt water spray.

From the above, it is readily apparent that the treating of anodized metal surfaces prior to sealing or prior and subsequent to sealing, with an aqueous solution of a sulficient amount of the/corrosion inhibitor of the invention, preferably an aqueous solution of from about 0.1 to 0.5% of the inhibitor, affords excellent protection to the anodized surface against future corrosion by moisture.

This application is a continuation-in-part of my copending application Serial No. 845,496, filed October 9, 1959, now abandoned.

Having described the invention, what is claimed is:

1. The method of inhibiting corrosion of metal surfaces in contact with an aqueous medium which comprises effecting said contact in said aqueous medium in the presence of a corrosion inhibitor added thereto which is the product formed by the addition reaction of an organic amine selected from the group consisting of alkylamines wherein the alkyl radical has from 1 to 14 carbon atoms, ethanolamine, diethanolamine, triethanolamine, abietylamines, and mixtures thereof with a mixture of a monobasic and a dibasic acid having the formula 0 2) x ly I wherein R is a radical selected from the group consisting of lower alkyl having from 1 to 6 carbon atoms, lower alkoxy-substituted lower alkyl having from 1 to 6 carbon atoms, phenyl and benzyl radicals, x is an integer selected from the group consisting of 2 and 3, and y and z are integers selected from the group consisting of 1 and 2, and the sum of y and z is 3, said corrosion inhibitor being present in said aqueous medium in an amount sufiicient to inhibit corrosion of said metal surfaces, and the amount of said organic amine reacted with said acid mixture is at least sufiicient to react and bind with the primary acid hydrogens of said mixture.

2. The method of inhibiting the corrosion of metal surfaces as defined in claim 1 wherein the amount of said organic amine reacted with said acid mixture is sufficient to react and bind with the primary acid hydrogens of said acid mixture.

3. The method of inhibiting the corrosion of metal sur- 1 1 faces as defined in claim 1 wherein the amount of said organic amine reacted with said acid mixture is suificient to react and bind with the primary acid hydrogens and about one-half of the secondary acid hydrogens.

4. The method of inhibiting the corrosion of metal surfaces as defined in claim 1 wherein said corrosion inhibitor is present in the amount of from 0.1 to 0.5% by weight.

5. The method of inhibiting the corrosion of metal surfaces as defined in claim 1 wherein the amount of said organic amine reacted with said acid mixture is at least sufficient to react and bind with the primary acid hydrogens of said acid mixture and not greater than the amount necessary to bind all of the acid hydrogens of said acid mixture.

6. The method as defined in claim wherein said metal surfaces are aluminum surfaces.

7. The method as defined in claim 5 wherein said metal surfaces are steel surfaces.

8. The method of inhibiting corrosion of metal surfaces in contact with an aqueous medium as defined in claim 5 wherein said metal surface is an aluminum surface, said organic amine is diethanolamine and said acid mixture is a mixture of monobasic and dibasic 2-butoxyethyl acid phosphates.

9. The method of inhibiting corrosion of metal surfaces in contact with an aqueous medium as defined in claim 5 wherein said metal surface is an aluminum surface, said organic amine is diethylamine and said acid mixture is a mixture of monobasic and dibasic 2-benzyloxyethyl acid phosphates, and said corrosion inhibitor is present in an amount of from 0.4 to 1.0% by weight.

10. The method of inhibiting corrosion of metal surfaces in contact with an aqueous medium as defined in claim 5 wherein said metal surface is an aluminum surface, said organic amine is dipropylamine and said acid mixture is a mixture of monobasic and dibasic 2-butoxyethyl acid phosphates, and said corrosion inhibitor is present in an amount of from 0.04 to by weight.

11. The method of inhibiting corrosion of metal surfaces in contact with an aqueous medium as defined in claim 5 wherein said metal surface is an aluminum surface, said organic amine is dibutylamine and said acid mixture is a mixture of monobasic and dibasic 2-butoxyethyl acid phosphates, and said corrosion inhibitor is present in an amount of from 0.04 to 1.0% by weight.

12. The method of inhibiting corrosion of aluminum surfaces in contact with an aqueous medium which comprises effecting said contact in said aqueous medium in the presence of from 0.04 to 1.0% by weight of a corrosion inhibitor which is a diethylamine salt of a mixture of butoxyethyl dihydrogen phosphate and bis(butoxy ethyl) hydrogen phosphate, said mixture having at least the primary acid hydrogens thereof reacted to and bound by said diethylamine.

13. The method of inhibiting corrosion of steel surfaces in contact with an aqueous medium which comprises effecting said contact in said aqueous medium in the presence of from 0.04 to 1.0% by weight of a corrosion inhibitor added thereto which is a diethylamine salt of a mixture of butoxyethyl dihydrogen phosphate and bis- (butoxyethyl) hydrogen phosphate, said mixture having at least the primary acid hydrogens thereof reacted to and bound by said diethylamine.

14. The method of inhibiting corrosion of aluminum surfaces in contact with a Water-ethylene-glycol medium which comprises effecting said contact in said medium in the presence of an effective amount added thereto of from 0.04 to 1.0% by weight of the diethylamine salt of an acid mixture of butoxyethyl dihydrogen phosphate, and bis(butoxyethyl) hydrogen phosphate, said mixture having at least the primary acid hydrogens thereof reacted to and bound by said diethylamine.

15. The method of inhibiting corrosion of steel surfaces in contact with a water-ethylene-glycol medium which comprises effecting said contact in said medium in the 12. presence of an effective amount added thereto of from 0.04 to 1.0% by weight of the diethylamine salt of an acid mixture of butoxy-ethyl dihydrogen phosphate, and bis(butoxyethyl) hydrogen phosphate, said mixture having at least the primary acid hydrogens thereof reacted to and bound by said diethylamine.

16. A corrosion-inhibiting composition for inhibiting corrosion of metal surfaces consisting essentially of an aqueous medium having therein an effective amount of the product formed by the addition reaction of an organic ,amine selected from the group consisting of alkylamines wherein the alkyl radical has from 1 to 14 carbon atoms, ethanolamine, diethanolamine, triethanolamine, abietylamines, and mixtures thereof with a mixture of a monobasic and a dibasic acid having the formula [R0 (CH2) obi (on) 1 wherein R is a member selected from the group consisting of lower alkyl having from 1 to 6 carbon atoms, lower allcoxy-substituted lower alkyl having from 1 to 6 carbon atoms, phenyl and benzyl radicals, x is an integer selected from the group consisting of 2 and 3, y and z are integers selected from the group consisting of l and 2, and the sum of y and z is 3, and the amount of said organic amine reacted with said acid mixture is at least sufficient to react and bind with the primary acid hydrogens of said acid mixture.

17. A corrosion-inhibiting composition for inhibiting corrosion of aluminum surfaces consisting essentially of an aqueuous medium having therein an eifective amount within the range of from 0.04 to 1.0% by weight of the product formed by the addition reaction of an organic amine selected from the group consisting of alkylamines wherein the alkyl radical has from 1 to 14 carbon atoms, ethanolamine, diethanolamine, triethanolamine, abietylamines and mixtures thereof with a mixture of a monobasic and a dibasic acid having the formula wherein R is a member selected from the group consisting of lower alkyl having from 1 to 6 carbon atoms, lower alkoxy-substituted lower alkyl having from 1 to 6 carbon atoms, phenyl and benzyl radicals, x is an integer selected from the group consisting of 2 and 3, y and z are integers selected from the group consisting of 1 and 2, and the sum of y and z is 3, the amount of said organic amine reacted with said acid mixture being at least sufficient to bind the primary acid hydrogens and no greater than that necessary to bind all of the acid hydrogens of said acid mixture.

18. A corrosion-inhibiting composition for inhibiting corrosion of aluminum surfaces as defined in claim 17 wherein said organic amine is diethylamine and said acid mixture is a mixture of monobasic and dibasic 2-butoxyethyl acid phosphates.

19. A corrosion-inhibiting composition for inhibiting corrosion of aluminum surfaces as defined in claim 17 wherein said organic amine is diethanolamine and said acid mixture is a mixture of monobasic and dibasic 2- butoxyethyl acid phosphates.

20. A corrosion-inhibiting composition for inhibiting corrosion of aluminum surfaces as defined in claim 17 wherein said organic amine is butylamine and said acid mixtureis a mixture of monobasic and dibasic 2-butoxyethyl acid phosphates.

21. The corrosion-inhibiting composition for inhibiting corrosion of aluminum surfaces as defined in claim 17, wherein said product is present in an amount of from 0.1 to 0.5% by weight.

22. The method of inhibiting the corrosion of aluminum and steel surfaces which are exposed to: moisture which comprises contacting said surfaces with an effective amount of the product formed by the addition reaction of an organic amine selected from the group consisting of [R (CH2) xol li (OH) wherein R is a member selected from the group consisting of lower alkyl having from 1 to 6 carbon atoms, lower alkoxy-substituted lower alkyl having from 1 to 6 carbon 7 atoms, phenyl and benzyl radicals, x is an integer selected from the group consisting of 2 and 3, y and z are integers selected from the group consisting of 1 and 2, and the 7 sum of y and z is 3, the amount of said organic amine reacted with said acid mixture being at least sufiicient to bind the primary acid hydrogens and no greater than that necessary to bind all of the acid hydrogens of said acid mixture.

23. A liquid composition having aluminum pigment therein, said composition containing water and an amount sufiicient to inhibit the corrosion of said aluminum pigment in the presence of said water of the product formed by the addition reaction of an organic amine selected from the group consisting of alkyl amines wherein the alkyl radical has from 1 to 14 carbon atoms, ethanolamine, diethanolamine, triethanolamine, abietylamines and mixtures thereof with a mixture of a monobasic and dibasic acid having the formula wherein R is a radical selected from the group consisting of lower alkyl having from 1 to 6 carbon atoms, lower alkoxy-substituted lower alkyl having from 1 to 6 carbon atoms, phenyl and benzyl radicals, x is an integer selected from the group consisting of 2 and 3, and y and z are integers selected from the group consisting of l and 2, and the sum of y and z is 3, said corrosion inhibitor being present in said aqueous medium in an amount sufficient to inhibit corrosion of said metal surfaces, and the amount of said organic amine reacted with said acid mixture is at least sufiicient to react and bind with the primary acid hydrogens of said mixture.

24. The composition as defined in claim 23 wherein said liquid composition is a liquid paint composition.

25. The composition as defined in claim 24 wherein said organic amine is diethylamine and said acid mixture is a mixture of butoxyethyl dihydrogen phosphate and bis(butoxyethyl) hydrogen phosphate.

26. The composition as defined in claim 24 wherein said organic amine is diethylamine and said acid mixture 14 is a mixture of hexoxyethyl dihydrogen phosphate and bis(hexoxyethyl) hydrogen phosphate.

27. In the process of anodizing a metal surface and subsequently sealing said anodized surface by immersing it in water at a temperature of from about F. to 212 F., the improvement whereby the sealed surface is more resistant to corrosion by water comprising immersing said anodized metal surface, prior to said sealing step, in an aqueous solution of a corrosion inhibitor which is the product formed by the addition reaction of an organic amine selected from the group consisting of alkyl amines wherein the alkyl radical has from 1 to 14 carbon atoms, ethanolamine, diethanolamine, triethanolamine, abietylamines and mixtures thereof with a mixture of a monobasic and dibasic acid having the formula I K QX L N M wherein R is a radical selected from the group consisting of lower alkyl having from 1 to 6 carbon atoms, lower alkoxy-substituted lower alkyl having from 1 to 6 carbon atoms, phenyl and benzyl radicals, x is an integer selected from the group consisting of 2 and 3, and y and z are integers selected from the group consisting of 1 and 2, and the sum of y and z is 3, said inhibitor being present in said aqueous solution in an amount sufficient to improve the resistance of said metal surface to corrosion by water.

28. The process as defined in claim 27 wherein said metal surface is an aluminum surface.

29. The process as defined in claim 27 wherein said metal surface is a magnesium surface.

30. The process as defined in claim 27 wherein said anodized metal surface is also immersed in said aqueous solution of said corrosion inhibitor subsequent to said sealing step.

31. The process as defined in claim 27 wherein said organic amine is diethylamine and said acid mixture is a mixture of butoxyethyl dihydrogen phosphate and his (butoxyethyl) hydrogen phosphate.

32. The process as defined in claim 27 wherein said organic amine is diethylamine and said acid mixture is a mixture of hexoxyethyl dihydrogen phosphate and his (hexoxyethyl) hydrogen phosphate.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF INHIBITING CORROSION OF METAL SURFACES IN CONTACT WITH AN AQUEOUS MEDIUM WHICH COMPRISES EFFECTING SAI CONTACT IN SAID AQUEOUS MEDIUM IN THE PRESENCE OF A CORROSION INHIBITOR ADDED THERETO WHICH IS THE PRODUCT FORMED BY THE ADDITION REACTION OF AN ORGANIC AMINE SELECTED FROM THE GROUP CONSISTING OF ALKYLAMINES WHEREIN THE ALKYL RADICAL HAS FROM 1 TO 14 CARBON ATOMS, ETHANOLAMINE, DIETHANOLAMINE, TRIETHANOLAMINE, ABIETYLAMINES, AND MIXTURES THEREOF WITH A MIXTURE OF A MONOBASIC AND A DIBASIC ACID HAVING THE FORMULA 